Set datastore's .hs field in SQLBaseStore rather than in the toplevel DataStore mixed-in result class

synapse/storage/__init__.py

@@ -44,7 +44,6 @@ class DataStore(RoomDataStore, RoomMemberStore, MessageStore, RoomStore,
     def __init__(self, hs):
         super(DataStore, self).__init__(hs)
         self.event_factory = hs.get_event_factory()
-        self.hs = hs
 
     def persist_event(self, event):
         if event.type == MessageEvent.TYPE:

synapse/storage/_base.py

@@ -27,6 +27,7 @@ logger = logging.getLogger(__name__)
 class SQLBaseStore(object):
 
     def __init__(self, hs):
+        self.hs = hs
         self._db_pool = hs.get_db_pool()
 
     def cursor_to_dict(self, cursor):